clang/test/SemaTemplate/instantiate-expanded-type-constraint.cpp

   1 // RUN:  %clang_cc1 -std=c++2a -verify %s
   2
   3 template<typename T, typename U>
   4 constexpr bool is_same_v = false;
   5
   6 template<typename T>
   7 constexpr bool is_same_v<T, T> = true;
   8
   9 template<typename T, typename U>
  10 concept same_as = is_same_v<T, U>;
  11 // expected-note@-1{{because 'is_same_v<int, _Bool>' evaluated to false}}
  12
  13 template<typename T, typename... Us>
  14 concept either = (is_same_v<T, Us> || ...);
  15
  16 template<typename... Ts>
  17 struct T {
  18     template<same_as<Ts>... Us>
  19     // expected-note@-1{{because 'same_as<int, _Bool>' evaluated to false}}
  20     static void foo(Us... u, int x) { };
  21     // expected-note@-1{{candidate template ignored: deduced too few arguments}}
  22     // expected-note@-2{{candidate template ignored: constraints not satisfied}}
  23
  24     template<typename... Us>
  25     struct S {
  26         template<either<Ts, Us...>... Vs>
  27         static void foo(Vs... v);
  28     };
  29 };
  30
  31 int main() {
  32   T<int, bool>::foo(1); // expected-error{{no matching function for call to 'foo'}}
  33   T<int, bool>::foo(1, 2, 3); // expected-error{{no matching function for call to 'foo'}}
  34   T<int, bool>::S<char>::foo(1, 'a');
  35   T<int, bool>::S<char>::foo('a', true);
  36 }